SEPTEMBER, 1962
NOTES
P-Terpinene and p-Phellandrene from the Pyrolysis of Sabinene 13. M. MITZNER AND E. T. THEIMER
3359
by n.m.r. and infrared as p-phellandrene, identical wit,h I11 isolated from a natural ~ o u r c e . ~ Experimental
Research Laboratories, Tntmnalional Flavors & Fragrances Trrc., Union Beach, New Jersey Received April 6, 1962
The only reported synthesis of 6-terpinene (I) is that of Wallach2 in five steps from sabinene (11). p-Phellandrene (111) has not been unequivocally synt,hesized, but is found in n a t ~ r e . ~ We have observed that 11, when pyrolyzed a t 600°, undergoes fission of the cyclopropane ring and forms I and 111:
Oil of savin was fractionated through a 2-ft. stainless steel protruded packed column, yielding sabinene-b.p. 45” :it 10 mm. and was analyzed pure by gas chromatography. This was passed four times through a 1 ft. X ]/E in. o.d., 2/32 inch i.d., stainless steel tube heated to 600°, a t a rate of 1 ml./min. A small flow of nitrogen was eniployed ae a carrier. The pyrolyzate was then separated into its components on a preparative gas chromatograph using a 3/8 in. 0.d. column packed with Reoplex 400 (207,) on 60-80 mesh silane treated Celite a t 100’. In this way, 8-terpinene and 8-phellandrene and unconverted sabinene are easily separable. We have found that it is essential that a non-acid type of solid support be used, otherwise a- and yterpinene will be formed from the 8-terpinene. p-Terpinene polymerizes in a matter of hours, especially when pure.
Acknowledgment.-The authors wish to acknowledge the aid given to them by Dr. S. Lemberg, of this laboratory, for his aid in the preparat,ion and interpretation of the n.m.r. spectra. I1
L
IV
A
I
I11
We postulate t,he biradical IV as an intermediate. The pyrolyzate from sabinene consists of a mixture of products including two major components, gas chromatographically eluted after the unconverted sabinene in an approximate ratio of 6:4. N.m.r. and infrared analysis confirm the structure of the first of these two peaks as P-terpinene. The n.m.r. spectrum of the p-terpinene indicated the following (in r values, tetramethylsilane, T = 10.00): 9.03, doublet, J c H ~H, 6 c.P.s., isopropyl group; 7.95, 7.87, 7.76, diffuse multiplet, allylic methylene; 7.28 multiplet, CH2 flanked by allylic double bonds; 5.36 singlet vinylidene methylene, > C = CHZ; 4.70 singlet, ring olefinic proton. The infrared spectrum of p-terpinene is characterized by a strong absorption a t 883 due to the >C=CHZ group which is also found in 1,(7) p-menthene. A medium band is observed a t 812 R* RB
(4) p-Phellandrene isolated from gum turpentine, and purified oio preparative gas chromatography. The sample wao graciously s u p plied by Mr. Ray V. Laurence, Chief, Naval Stores Laboratory: Olustee, Florida.
Absence of Asymmetric Induction in the Lithium Aluminum Hydride-&Camphor Reduction of Ketones PHILIP S. PORTOGHESE Department of Pharmaceutical Chemistry, College of Pharmacy, University of Minnesota, Minneapolis 14, Minnesota Received April 9, 1962
The exact mechanism of the reduction of ketones to secondary alcohols by lithium aluminum hydride is not known with certainty. I n an effort to elucidate the mode of hydride transfer to an electrophilic \ / cm.-1 which is due to the C=C group and center, we have employed the procedure of Bothner-By’ in which he has reported the preparation of / \ optically active secondary alcohols by reduction of R2 H is also found in 3, p-menthene. The split at 1375 the corresponding ketones. According to his ern.-’ is characteristic of the “gem” dimethyl group procedure, one equivalent of lithium aluminum hydride is reacted with two equivalents of d-camphor CHs whereupon the introduction of an unsymmetrical \/ C (found in both 1,(7) p-menthene as well ketone such as 2-butanone or pinacolone supposedly affords optically active 2-butanol or methyl-& /\ CHa butylcarbinol, respectively. I n repeating his exa s 3,p-menthenel. The second peak was identified perimental procedure we have observed no evidence of asymmetric induction in the hydride (1) a-Terpinene has not been positively identified in natural reduction of 2-butanone and pinacolone. materials. .r
(2) 0. Wallach. Ann., 867, 69 (1907). (3) J. L. Simonaen, “The Terpenes,” Vol. I, Cambridge, England,
University Press, 1963, p. 204.
(1) A. A. Bothner-By, J . Am. Cham. S O O . , ~ ? 846 ~ , (1951).
NOTES
3860
The separation of 2-butanol and methyl-tbutylcarbinol from d-isoborneol was accomplished by first distilling through a six-inch Vigreux column and subsequently fractioning through a 23-plate spinning band column. Both alcohols were found to be optically inactive. It is possible that in the procedure employed by Bot~hner-By,' separation of 2-but,anol and methyl-t-butylcarbinol from small quantities of optically active material was incomplete and consequently caused the observed positive rotation.2 In a recent communication, Elie13 has presented evidence for a possible disporportionation step in with the reduction of 3,3,5-trimethylcyclohexarione lithium aluminum hydride. If this is of general consequence in the reduction of ketones to secondary alcohols, perhaps the production of racemic alcohols from ketones with lithium aluminum hydride-d-camphor is indicative of attack by rather than A1(OR)?H2-. Thus during the reduction of two equivalents of d-camphor by one equivalent of lithium aluminum hydride, the initially formed AI(OR)H,- can conceivably be transformed to A1H4- via a disproportionation step.3 Since AI(OR)H,- is not as effective as reducing agentj4AIH4- could act as the reducing species even in the presence of a substantial quantity of alkoxyhydride anion. Experimental Reduction of 2-Butanone.-A solution of 30 g. (0.2 mole) of d-camphor in 50 ml. of ether was dropped with stirring over a 0.5-hr. period into a solution of 3.8 g. (0.2 mole) of lithium aluminum hydride in 300 ml. of ether. This was followed by a 0.5-hr. addition of 15 ml. (0.2 mole) of 2butanone in 50 ml. of ether. To the above mixture there was added 100 ml. of 17% hydrochloric acid followed by several grams of sodium chloride so as to facilitate separation of the ether layer. The organic phase was dried over calcium chloride and subsequently with calcium hydride. The ether was distilled from a mixture on a steam bath and 15 ml. of xylene added to the residue. Distillation through a 6-in. Vigreux column followed by two fractionations through a 23-plate spinning band column afforded 5 mI. of 2-butanol; b.p. 99'(750mm.), nZ6' 1.3952, [a]*%O'. Reduction of Pinacolone.-Pinacolone, 20 g. (0.2 mole), was reduced in a manner identical to that of 2-butanone. After treatment with 100 ml. of 17% hydrochloric acid the ether solution was dried over calcium chloride and the solvent removed by distillation. To the residue was added 15 ml. of dwalin and the methyl-t-butylcarbinol distilled through a &in. Vigreux column. Two subsequent fractionations through a 23-plate spinning band column gave 7 ml. of methyl-t-butylcarbinol; b.p. 119-119.5 (748 mm.), 12% 1.4127, [ a ] % D 0 " .
12) I n recent private communication, Dr. Bothner-By has expresqed his agreement with us ooncerning the absence of aaymmetric induction in the d-camphor-lithium aluminum hydride reduction of 2-butanone and pinacolone. (3) E. L. Eliel end H. Haubenstock, dbstracts of papers presented at 141st National Meeting, American Chemical Society, p. 11-0. (4) H. C. Brown and R. F. McFarlin. J . Am. Chem. SOC.,80, 5372
(1968).
YOL.
27
Acidity of Hydrocarbons. VI. JIetalation of Norbornadiene with Butyllithiuml A. STREITWIESER, J R . , AND ~ R. A. CALDWELL Department of Chemistry, University of California, Berkeley, Califomin Heceived April 9, 1962
Wittig and Hahn3hare reported that the reactioii of norbornadiene with equimolar butyllithium gives products expected from the ion-pairs, I, 11, and IIT. We have performed similar experiments in
n 111
order to obtain evidence relating to the relative acidities of the various hydrogens in norbornadiene. Of particular interest is the relative mobility of the 7-hydrogens (bridge) because simple MO calculations predict no delocalization energy for the anion IV.
Sorbornadiene was allowed to react with excess butyllithium in refluxing ether-heptane. After quenching with deuterium oxide, the recovered norbornadiene was studied by infrared and n.m.r. S o evidence was obtained for significant abstraction of a 7-hydrogen, in qualitative agreement with the molecular orbital prediction. The reaction mixture had typically a magenta color (A, 560 mp). The product mixture as analyzed by gas chromatography contained norbornadiene and high-boiling materials, presumably the butylated products reported by Wittig and Hahn.3 Korbornadiene as separated by gas chromatography showed vinyl deuterium in amounts depending on the duration of the reaction (Table I). In the product of the ten-hour reaction the (1) Paper V, A. Streitwiaser, Jr., D. E. Van Sickle, and L. Reif, J . Am. Chem. Soc., 84, 258 (1962). This research was slipported in part by an Air Force Grant, AFOSR-62-175. (2) Alfred P. Sloan Fellow, 1958-1962. (3) G. Wittig and E.Hehn, Anpew. Chem., 72, 781 (1960).
